refactor: rename content types to semantic taxonomy

- vault → notes (PKM-exported content)
- posts → articles (short-form, no TOC)
- papers → essays (long-form, with TOC)
- type: post → type: article (posts are just short articles)
- layouts/paper → layouts/essay
- 08a-paper.css → 08a-essay.css
- CSS: fix redundant li resets, remove role="main" from article,
  replace <small> prev/next labels, add console layout
- Update hugo.toml menus, internal URLs, front matter throughout
- Add docs/context.md, docs/css-refactor-plan.md

content/vault/tasks.md

@@ -1,38 +0,0 @@
----
-title: "Tasks"
-description: "Render task lists with semantic state: done, wip, blocked, todo."
-section: vault
-prev-url: ""
-prev-title: ""
-next-url: "wikilinks/"
-next-title: "Wikilinks"
-type: vault
-date: 2026-04-09
-tags: ["vault", "tasks", "reference"]
-ai-disclosure: "generated"
-ai-model: "claude-sonnet-4-5"
-ai-provider: "Anthropic"
-
----
-
-## Overview
-
-Use `data-task` on list items to convey task state without CSS classes.
-
-```html
-<ul>
-  <li data-task="done">Completed item</li>
-  <li data-task="wip">Work in progress</li>
-  <li data-task="blocked">Blocked item</li>
-  <li data-task="todo">Not started</li>
-</ul>
-```
-
-## States
-
-| Value | Meaning |
-|-------|---------|
-| `done` | Completed — green check |
-| `wip` | In progress — amber |
-| `blocked` | Blocked — red |
-| `todo` | Not started — muted |